Aquaculture Effluents as Fertilizer in Hydroponic Cultivation
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Transcript of Aquaculture Effluents as Fertilizer in Hydroponic Cultivation
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Aquaculture Effluents as Fertilizer in Hydroponic Cultivation A Case Study Comparing Nutritional and Microbiological Properties Johan Lund
Sjlvstndigt arbete 15 hp Hortonomprogrammet Alnarp 2014
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Aquaculture Effluents as Fertilizer in Hydroponic Cultivation: A Case Study Comparing Nutritional and Microbiological Properties Fiskodlingsvatten som nringsklla i hydroponisk odling: En fallstudie som jmfr nrings-mssiga och mikrobiologiska egenskaper
Johan Lund Handledare: Beatrix Alsanius, SLU, Institutionen fr Biosystem och teknologi Examinator: Sammar Khalil, SLU, Institutionen fr Biosystem och teknologi Omfattning: 15 hp Niv och frdjupning: G2E Kurstitel: Kandidatarbete i trdgrdsvetenskap Kurskod: EX0495
Program/utbildning: Hortonom Examen: Kandidatarbete i Trdgrdsvetenskap mne: Trdgrdsvetenskap (EX0495) Utgivningsort: Alnarp Utgivningsmnad och r: Mars 2014 Omslagsbild: Frfattarens bearbetning av bilden
http://www.flickr.com/photos/thart2009/5376510119/sizes/l/ av Tom Hart. Licens CC-BY-SA. Elektronisk publicering: http://stud.epsilon.slu.se
Nyckelord: Organic hydroponic. Aquaponic. Aquaculture. Plant nutrition. Microbial horticul-
ture. SLU, Sveriges lantbruksuniversitet Fakulteten fr landskapsarkitektur, trdgrds- och vxtproduktionsvetenskap Institutionen fr biosystem och teknologi
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Sammanfattning
Detta arbete utvrderar mjligheterna att anvnda vattnet frn fiskodlingar som nringskl-
la i ekologisk hydroponisk odling, s som r fallet i akvaponiska odlingssystem. Att erstta
syntetiska gdselmedel med organiska r avgrande fr utvecklingen av ekologisk hydro-
ponisk odling. Dessutom ingr etablering av en sjukdomsundertryckande mikroflora som
en del av vxtskyddsstrategin i moderna hydroponiska odlingar. Drfr analyserades och
jmfrdes bde nringsmssiga och mikrobiella egenskaper hos fiskodlingsvatten med de
frn en ekologisk hydroponisk nringslsning. Resultaten visade att bde den hydroponis-
ka nringslsningen och fiskodlingsvattnet hade brist p flertalet essentiella vstnrings-
mnen, dock var den ekologiska nringslsningen mest optimal. Den ekologiska nrings-
lsningen hade hgst densitet av aeroba bakterier, s vl som av fluorescerande pseudo-
monader. Nivn av svampar var likvrdig. Halten av fluorescerande pseudomonader var
mrkbart mindre efter att fiskodlingsvattnet passerat anlggningens biofilter.
En kvalitativ analys av mikrofloran i en akvaponisk odling skulle kunna ka frstelsen
av mikroorganismers upptrdande i denna unika milj samt potentiell inverkan p vxt-
skydd och vxtnringscykeln.
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Abstract
This paper evaluates the prospects for utilizing aquaculture effluents as a nutrient source in
organic hydroponic, as is the case in aquaponics. The development of organic hydroponics
is dependent on replacing synthetic fertilizers with organically derived nutrients, such as
those found in aquaculture effluents. Also, in hydroponic cultivation the establishment of a
plant pathogen suppressive micro flora is part of the plant protection strategy. Therefore,
both nutritional and microbial qualities of aquaculture water and organic hydroponic nutri-
ent solution were analyzed and compared. Results showed both aquaculture water and or-
ganic hydroponic solution to be deficient in a number of essential elements, although or-
ganic hydroponic solution was closer to recommendations. The organic nutrient solution
had the highest densities of aerobic bacteria as well as fluorescent pseudomonades. Levels
of fluorescent pseudomonades in aquaculture water were significantly lower after passing
through the biofilter. Qualitative analysis of microorganisms in an actual aquaponic farm
would help to better understand the composition of the micro flora in this unique environ-
ment and its implications for nutrient cycling as well as plant health.
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Table of contents
1 Introduction 1 1.1 Purpose of study ........................................................................................................... 2 1.2 Hypothesises ................................................................................................................ 2
2 Background 3 2.1 Aquaculture effluents as a nutrient source for hydroponic cultivation systems ............. 3 2.2 The role of microbes in hydroponic cultivation systems. ............................................... 5
3 Materials and Methods 7 3.1 Samples ........................................................................................................................ 7 3.2 Microbiological analyses ............................................................................................... 7
3.2.1 Treatments ........................................................................................................ 7 3.2.2 Preparations, dilutions and plating ..................................................................... 8 3.2.3 Analysis ............................................................................................................. 8 3.2.4 Sources of error ................................................................................................. 9
3.3 Chemical Analyses ....................................................................................................... 9 3.4 Statistical Analyses ..................................................................................................... 10
3.4.1 Analysis of microbiological parameters ........................................................... 10
4 Results 11 4.1 Results from Chemical Analysis ................................................................................. 11 4.2 Results from Microbiological Analysis ......................................................................... 13
5 Discussion 14 5.1 Nutritional qualities of aquaculture water compared to organically derived nutrient
solution. ...................................................................................................................... 14 5.2 Microbial densities ...................................................................................................... 15
6 Conclusion 17
7 References 18 7.1 Literature ..................................................................................................................... 18 7.2 Manuals ...................................................................................................................... 19
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1 Introduction
Aquaculture is the fastest growing sector of all animal food production. From
2000 to 2008 production almost doubled. Nearly half of the fish consumed glob-
ally is provided by aquaculture, and a majority of this comes from freshwater sys-
tems (FAO, 2011). The discharge of aquaculture effluents and raised competition
over the use of freshwater is identified as some of the main issues of environ-
mental concern associated with open and flow-through aquaculture. (FAO, 2006)
(FAO, 2011) Recirculating aquaculture systems on the other hand, is an example
of water efficient food production (FAO, 2011). In recirculating aquaculture sys-
tems, great numbers of fish are cultured in minimal volumes of water. The same
water is recirculated repeatedly and must be treated in a biological filter to avoid
toxic levels of nitrogenous waste products. The process of reusing treated water
results in accumulation of mineral nutrients and organic matter. If daily water ex-
change is less than two percent of the total volume, nutrients accumulate in con-
centrations close to levels found in hydroponic nutrient solutions (Rakocy et al.,
2006).
In hydroponic growing systems plants are cultivated in small containers, gutters or
mats with a majority of the nutrients supplied by a liquid medium (Savvas, 2003).
Closed hydroponic systems waste very little water and fertilizer. Despite the ad-
vantages of recycling nutrients and water, most growers worldwide use open sys-
tems to reduce the risk of disease (Carruthers, 2007). When growers first adopted
the hydroponic technology the ideal was a sterile system, free from microorgan-
isms. This proved impossible. New pathogens emerged, thriving in the liquid me-
dium with little competition from other microorganisms (Postma et al., 2008). The
modern approach in closed hydroponic systems is to use biological control meth-
ods to fight and prevent disease (Atkin & Nichols, 2004).
Consumers and governments push for food that is safe, nutritious and sustainable
(Carruthers, 2007). Organic hydroponics can offer products that might meet these
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criteria. With respect to efficient resource use and biological pest management,
hydroponic systems are already well developed. If soilless cultivation can be ac-
cepted in the organic standards, the major challenge for organic hydroponic is to
replace synthetic fertilizers with those derived from organic sources (Atkin &
Nichols, 2004). This paper compares the nutritional and microbiological properties
of the nutrient solution from a closed organic hydroponic with those of water from
a recirculating aquaculture facility to evaluate the suitability of aquaculture efflu-
ents as a source of organic fertilizer for hydroponic systems, as is the case in aq-
uaponic systems. Aquaponic culture integrates fish and hydroponic plant produc-
tion into one recirculating system. Most plant nutrients are provided by effluents
from the aquaculture subsystem. Aquaculture effluents are removed of nitrogenous
waste products in the hydroponic component and then returned. The same culture
water may be continuously recirculated for years (Rakocy et al., 2004). Successful
and sustainable integration requires optimizing growth of three integrated biologi-
cal components: fish, plant and nitrification bacteria. The challenge is to maximize
production and minimize release of nutrient loaded wastewater to the environment
(Tyson et al., 2011).
1.1 Purpose of study
The purpose of this study was to evaluate recirculated aquaculture water as a nu-
trient source for organic hydroponics.
1.2 Hypothesises
1. Water from the recirculating aquaculture system contains the highest density of
cultivable microorganisms, compared to the recirculating biosolid nutrient solu-
tion in the hydroponic facility.
2. The biosolid based nutrient solution used in the hydroponic facility is more nu-
tritionally optimized as lettuce fertilizer, than is water from the recirculating aq-
uaculture system.
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2 Background
2.1 Aquaculture effluents as a nutrient source for hydroponic cultivation systems
In this paper effluents from a recycling aquaculture system are compared to nutri-
ent solution from an organic hydroponic. Although this comparison can provide
useful information, utilizing aquaculture effluents in hydroponics is not feasible
with the two being separate systems. The real benefits first emerge when hydro-
ponics and aquaculture are fused into one closed system; an aquaponic system. A
well functioning system has to balance the needs of fish, plants and microorgan-
isms to maximize production outputs and minimize pollution (Tyson et al., 2011).
Great advantages with aquaponic are that fish effluents become a resource for
plants, and plants treat the water (Rakocy et al., 2006). A challenge is that nitrifi-
cation and plant growth cannot be optimized simultaneously (Savidov, 2004) (Ty-
son, 2011). Table 1 displays the relationships between important environmental
parameters and the biological components of an aquaponic system.
Table 1. Relation between environmental parameters and biological components in aquaponic sys-
tems.
Parameters Fish Nitrification bacteria Plant
pH 5.5- 6.5 Below optimal levels
of performance. 1
Optimal for plant
growth and mineral
nutrient solubility.1
pH 7.5 -8.0 Optimal performan-
ce.1
Essential mineral
nutrients less avail-
able.2
Ammonia Excreted by fish,
toxic at low con-
centrations.3
Remove ammonia by
nitrification. 3
Plants absorbing
ammonium reduce
levels of ammonia
in water. Source of
nitrogen for plants.1
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Nitrate Relatively non
toxic for fish.3
Final product from
the full bacterial nitri-
fication of ammonia.
Process that demands
oxygen 3
Main source of
nitrogen for plants.1
Mineral nutrients Excreted by fish,
accumulate in
recirculating
water.2
Absorbed by plants,
essential for growth
and development. 2
1.Tyson et al (2011).
2. Rakocy et al. (2006).
3. Hagopian & Riley (1998).
Nitrogen is vital for plant growth and the mineral nutrient required in largest
amount (Taiz & Zeiger, 2006). Sixty to ninety percent of nitrogenous waste in
aquaculture are in the form of ammonia (NH3) and ammonium (NH4), originating
from the gills of the fish. Urine, feces, gill cation exchange and uneaten feed also
contributes to total nitrogenous waste loading in aquaculture. In the case of tank
reared fish, very small amounts of feed remain uneaten (Hagopian & Riley, 1998)
Part of the ammonia excreted is ionized into ammonium and these two forms to-
gether make up the total ammonia nitrogen, abbreviated TAN (Figure 1) (Tyson et
al., 2011).
Figur 1. Total ammonia nitrogen (TAN) equilibrium in water (Tyson et al., 2011).
Unionized ammonia is toxic to fish even at low concentrations and must not ac-
cumulate in the recirculating water. The same applies to nitrite, but lethal concen-
trations vary substantially between species and stages in the life cycle of fish. Ni-
trate on the other hand, in some cases, can exceed the toxic levels of ammonia a
million times before reaching lethal concentrations. Thus the full nitrification of
ammonia and nitrite is an essential part of the recirculating aquaculture system
(Hagopian & Riley, 1998). In the aquaponic system, potentially toxic ammonia is
removed both by microbial activities and by phytoremediation (Tyson et al.,
2011).
In general, all mineral plant nutrients except calcium, potassium and iron are
present in adequate amounts in aquaculture effluents, according to Rakocy et al.
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(2004). Minimizing daily water exchange is important to achieve accumulation of
mineral nutrients (Rakocy et al., 2006). Keeping pH above 7.0 is the key to effec-
tive nitrification, but the process itself lowers pH. To compensate for the low pH,
and at the same time raise levels of calcium and potassium, Rakocy et al. (2004)
continuously added Ca(OH)2 and KOH to their aquaponic system. Iron deficiency
was avoided by adding iron chelate. Fish waste provided all other nutrients in this
experiment. Tyson et al. (2011) also emphasized the importance of effective nitri-
fication, suggesting pH 7.5-8.0 rather than at optimum for plant mineral nutrient
solubility in the range pH 5.5-6.5, for water quality to remain high. Savidov
(2004) argued for another strategy in which pH is decreased to 6.2. At this level
mineral nutrients are more soluble and plant growth is favored. Savidov (2004)
showed that plants are very effective as the main nutrient control mechanism in
aquaponics, absorbing ammonium very fast. As well, at acidic pH the TAN equi-
librium is weighted towards ammonium, decreasing levels of free ammonia
(Savidov, 2004). Ammonium is a source of nitrogen, but in high levels it is toxic
to plants. Ammonium also affects the plant indirectly. When assimilated by the
roots, a lot of oxygen is consumed. A well aerated root environment, such as in
soilless cultivation, facilitates assimilation of ammonium. (Silber & Bar-Tal,
2008:307-310). Also, ammonium depresses the uptake of potassium, calcium and
magnesium. (Marschner, 1995: 38-39)
By regulating pH with phosphoric acid, potassium can be supplemented to
meet plant demand without affecting pH (Savidov, 2004). Calcium and magnesi-
um were abundant in the local water and available in adequate amounts at the low-
er pH. Fe was supplemented (Savidov, 2004). Savidov (2004) identifies imbal-
anced fish feed as the source of deficiency in aquaponics and suggests developing
plant based fish feed with higher levels of potassium.
2.2 The role of microbes in hydroponic cultivation systems.
It has become evident that a soilless growing system free of microbes is unrealistic
and emphasis has been shifted towards establishing a micro flora that suppresses
plant pathogens (Postma, 2004). A lot of research has been done to quantify and
identify microorganisms and their influence on suppressing plant pathogens and
plant disease attacks in different hydroponic systems (Vallace et al., 2010). Mi-
croorganisms in soilless culture can inhabit growing media, nutrient solution and
rhizosphere. Diversity and density of microbes in the respective habitat is affected
by growing media, nutrient solution and age and cultivar of plant species (Vallace
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et al., 2010). The micro flora can act to suppress pathogens by competition, para-
sitism, antibiosis and systemic induced resistance in the plant (Vallace et al.,
2010). Studies of the micro flora in aquaponics have so far focused on nitrifiers
and their role in nitrification (Tyson et al., 2011). But establishment of plant path-
ogens should be of no less concern in aquaponics than in hydroponics. Patterns of
microbial diversity and density in the aquaponic system could be expected to dif-
fer from those in hydroponic cultures. Therefore the micro floras of aquaponic
cultures need to be studied from the perspective of disease suppression as well as
nitrification.
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3 Materials and Methods
3.1 Samples
Samples were collected in two separate facilities, a closed hydroponic greenhouse
system and a recirculating aquaculture system. Sampling occurred at three occa-
sions, every other week, in January and February 2012.
In the hydroponic greenhouse facility organically certified lettuce was produced.
Nutrient solution was circulated and based on bio-solids. Growing medium was
peat and production staggered. Solution samples were collected in 3 sterile glass
bottles (2L) from the nutrient solution tank and immediately placed in cool bags.
Water from recirculating aquaculture facility producing tilapia was collected at
two cardinal points: fish rearing tank outflow and from biofilter outflow. Three
sterile glass bottles (2L) where filled with water from each cardinal point and im-
mediately placed in cooler.
2 liter samples were collected for microbiological analysis and transferred to a
cool storage when arriving at the research facility. For each two liters of sample a
50 ml sample was collected as well, to be used for chemical analysis. These sam-
ples were stored in a freezer. Temperature was measured on site with infrared
thermometer.
3.2 Microbiological analyses
3.2.1 Treatments
The following three groups of heterotrophic microorganisms were analyzed: gen-
eral bacterial flora, general fungal flora and fluorescent pseudomonades. Groups
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of microbes were distinguished by different treatments (medium, incubation time,
incubation temperature) (Table 2).
To determine the density of cultivable microbes, each group was analyzed quanti-
tatively with regard to colony forming units (cfu) per volume (ml) of sample.
Table 2. Treatments for analysis of colony forming units(cfu).
Group to be ana-
lyzed
Medium Incubation tem-
perature (C)
Incubation time
(h)
Analysis
General bacterial
flora in water
samples.
R2A 25 48 Visual standard-
ized count of
bacterial cfu.
General fungal
flora
0.5 malt extract
(MA)
22 96 Visual standard-
ized count of
fungal cfu.
Fluorescent pseu-
domonades
King agar B
(KB)
25 24 Visual standard-
ized count of
fluorescent colo-
nies under UV
light.
3.2.2 Preparations, dilutions and plating
Samples of water and nutrient solution were serially diluted in 0.85 NaCl. From
each dilution step, 50l were spread in duplicates using a spiral plater. Plating was
performed mechanically using a WASP 2 apparatus (Whitley Automated Spiral
Plater 2, Don Whitley Scientific Limited, Shirley, UK).
3.2.3 Analysis
Colony forming units were quantified with a standardized counting procedure,
using a circular grid specially designed for manual counting of spiral plates. The
grid showed areas representing a dispersed volume of sample solution and was
placed over the petri dish for the counting of colony forming units. Starting from
the outside and working towards the center, the smallest area containing 30 cfu
was chosen for calculating density of viable microbes in the dispersed solution
(cfu ml-1
). Each area was duplicated radially opposite and together represent a
specified dispersed volume. Once the appropriate area for calculation was deter-
mined, a count of cfu in complementary areas was performed. If the largest desig-
nated area contained less than 30 cfu, total count of colony forming units was per-
formed. Three dilution levels were chosen to be plated for each sample and medi-
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um. The two replicates easiest to count, of the three dilutions of each sample, was
used for calculating density of viable cultivable microorganisms.
3.2.4 Sources of error
Samples collected were to be analyzed within 48 hours and kept cool during all
times. During the first cycle of sampling and analysis the spiral plater was mal-
functioning and no results were obtained at the first sampling. This means analysis
could not be performed within 48 hours. Water samples were used for additional
analyses, other than comprised in this paper, therefore sample bottles were used a
lot in the lab and not always kept cool.
An error occurred during plating in the second cycle. All petri dishes went in
the spiral plater before it was realized that the vacuum pump was not turned on,
with the effect that no volumes were sucked up and dispersed. Since the suction
tube is dipped in ethanol and rinsed twice during the plating procedure, it was de-
cided to use the same plates again. This increase the risk of contamination, but all
plates were exposed to the same treatment.
3.3 Chemical Analyses
Chemical parameters such as pH, electrical conductivity (EC) and mineral ele-
ments where analyzed externally (LMI, Sweden). Samples were sent to the labora-
tory for analysis as soon as possible after collection.
Total nitrogen (TN), ammonium, nitrite, nitrate and total organic carbon (TOC)
analysis was performed by using Lange Cuvette Tests (LCK) (Hach-Lange, USA)
(Products and equipment specified in Table 4.). The instructions on how to use the
individual kits for each parameter where followed and the designated cuvettes
where analyzed in a fully automated photo spectrometer, the LANGE XION500
(Hach-Lange, USA), calculating the results automatically. See Hach LANGE
manual for more information (Hach Lange, [online] 2012 -05 -28).
Table 3. Hach Lange (USA) products used to analyze chemical parameters.
Analyzed
Parameter
Product
name
Additional apparatus used for
preparing sample
Total Nitrogen
(TN)
LCK 338
Total Ni-
trogen
LANGE LT200 (Thermostat)
Ammonium LCK 303 None
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10
Ammonia
(2.5 -60.0
mg l-1)
Nitrate LCK 340
Nitrate (22
-155 mg l-1)
None
Nitrite LCK 342
Nitrite
(0.05 -20
mg l-1)
None
Total Organic
Carbon (TOC)
LCK 385
TOC (3 -30
mg l-1)
LANGE TOC-X5 (Shaker)
LANGE LT200 (Thermostat)
The timing of the sampling occasions should have been more carefully selected
with respect to fertilization and feeding cycles. Information on the last time nutri-
ents where added to the nutrient solution or when fish was last fed was not noticed
for any of the sampling occasions.
3.4 Statistical Analyses
3.4.1 Analysis of microbiological parameters
Differences in microbial density between hydroponic nutrient solution, fish rearing
tank water and biofilter effluent in relation to sampling occasion were tested using
ANOVA General Linear Model. Nutrient solution and aquaculture water were
compared on all shared parameters (19 chemical and physical, 3 microbiological)
using ANOVA General Linear Model. This model makes comparisons on three
levels: Sample site, sample occasion and selected parameter. Sample site was set
as a fixed factor and sampling occasion as a random factor. All sample sites were
categorized as independent. The Tukey method was used, on a 95.0 % confidence
level, to calculate significance between sample site means on all shared parameters
and to obtain grouping information. Minitab 16 (Minitab Inc, Pennsylvania, USA)
statistical software was used for statistical calculations.
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4 Results
4.1 Results from Chemical Analysis
Aquaponic showed low values on all parameters compared to standard nutrient
solution, except for manganese. The pH was corresponding better to the require-
ments of crop cultivation in aquaculture water than in the nutrient solution. Nitrate
levels were very low in all sampling sites, but were highest in nutrient solution.
Levels of ammonium were low as well, but closer to optimum in nutrient solution
than in water. The ratio of nitrate -ammonium was closer to recommendations for
plant cultivation in aquaculture water, but low in all samples (Table 4).
Table 4. Inorganic nitrogen, total organic carbon, pH and electrical conductivity (EC) of samples
compared to recommended hydroponic nutrient solution for cultivation of lettuce (Sonneveld &
Straver, 1994). Results obtained from LCK test when not specified otherwise. Different letters on
results means significant difference.
(mmol l-1) Hydroponic Fish tank
Biofilter
effluent.
Standard
nutrient
solution (25 C) Hydroponic
Biofilter Fish tank
pH1 7.20 a 6.17 b 5.83 b NA
EC1 (mS/cm) 2.24 a 0.78 b 0.76 b 2.6 -0.36 -1.82 -1.84
TOC 3.16 a 1.58 b 1.07 c NA
TN 11.16 a 4.89 b 5.05 c NA
Ammonia
(NH4) 0.79 a 0.40 b 0.34 b 1.25 -0.46 -0.85 -0.91
Nitrite (NO2) 0.29 a 0.00 b 0.00 b NA
Nitrate (NO3) 1.73 a 0.96 b 0.97 b 19 -17.27 -18.04 -18.03
NO3/NH4 2.20 2.40 2.87 15.20 -13.00 -12.80 -12.33
1 Results from external analysis (LMI, Sweden)
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Water from the the sample sites in the aquaculture system was deficient in all mac-
ronutrients and very low on phosporous and potassium. The nutrient solution
showed abundance of magnesium, sulfur and calcium, but deficiency of phospho-
rous, potassium and silicon. (Table 5).
Table 5. Essential macro elements from sample sites compared to recommended hydroponic nutrient
solution (Sonneveld & Straver, 1994).
Essential
elements
(mmol/l)
Hydroponic
mean
Fishtank
mean
Biofilter
mean
Standard
hydroponic
solution. Hydroponic
fish rearing
tank
biofilter
effluent
P 0,38 a 0,08 b 0,08 b 2,0 -1,62 -1,92 -1,92
K 5,39 a 0,42 b 0,42 b 11,0 -5,61 -10,58 -10,58
Mg 1,36 a 0,37 b 0,37 b 1,0 0,36 -0,63 -0,63
S 2,22 b 0,43 b 0,42 b 1,125 1,10 -0,70 -0,70
Ca 5,07 a 2,02 b 2,01 b 4,5 0,57 -2,48 -2,49
Si 0,38 a 0,16 b 0,16 b 0,5 -0,12 -0,34 -0,34
Of all essential elements in nutrient solution and aquaculture water that showed
deficiency compared to standard nutrient solution, nutrient solution was closer to
optimum. Aquaculture samples were deficient in all microelements except manga-
nese, with levels of molybdenum and iron to be considered very low. Nutrient so-
lution was deficient in boron and zinc, but abundant in microelements manganese,
copper, iron and molybdenum. Levels of manganese was abundant in all samples,
but highest in hydroponic medium (Table 6).
Table 6. Essential microelements from sample sites compared to recommended hydroponic nutrient
solution for lettuce cultivation (Sonneveld & Straver, 1994). Results obtained from external analysis
(LMI, Sweden)
Essential
elements
(mol/l)
Hydroponic Fishtank Biofilter
Standard
nutrient solu-
tion. Hydroponic
fish rearing
tank
biofilter
outflow
Mn 4.75 a 2.12 b 2.12 b 0.0 4.75 2.12 2.12
B 17.10 a 3.37 b 3.34 b 30 -12.90 -26.6 -26.7
Cu 2.41 a 0.26 b 0.23 b 0.75 1.66 -0.49 -0.52
Fe 59.86 a 0.60 b 0.75 b 40 19.86 -39.40 -39.25
Zn 2.68 a 2.10 a 2.08 a 4 -1.32 -1.904 -1.92
Mo 3.94 a 0.06 b 0.08 b 0.5 3.44 -0.44 -0,42
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4.2 Results from Microbiological Analysis
Total density of microorganisms was highest in the nutrient solution. Counts of the
general bacterial flora showed significant differences between the nutrient solution
and the aquaculture water, with highest numbers in the nutrient solution. No sig-
nificant difference was found between fungal counts in any sample site. The oc-
currence of fluorescent pseudomonades was significantly different between all
sample sites and most abundant in nutrient solution (Table 7).
Table 7. Microbial density of hydroponic and aquacultural water based on viable count. Values
within the same row followed by different letters are statistically different according to Tukeys-test
(p< 0.05).
log cfu ml-
1
Cultured mic-
robial groups
Hydroponic Fish tank Biofilter
MA Fungi 4.9a 5.3a 4.5a
R2A General bacte-
rial flora
6.5a 5.2b 4.8b
KB Fluorescent
pseudomonades
3.9a 2.3b 0.9c
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5 Discussion
5.1 Nutritional qualities of aquaculture water compared to organically derived nutrient solution.
In reference to recommended standard solution for the hydroponic cultivation of
lettuce (Sonnenveld & Straver, 1994) neither the organic nutrient solution nor the
aquaculture effluents provided the complete range of nutrients in sufficient
amounts. In comparison between the two locations, the nutrient solution was better
adapted to plant requirements on all parameters. The acidic pH suggests that bac-
terial nitrification in aquaculture biofilter was not working at the full potential.
Levels of essential elements deviate from recommended values and both aqua-
culture water and organic nutrient solution might seem inadequate as nutrient
sources for hydroponic cultivation. But in organic hydroponic the liquid medium
is not the only nutrient source. According to the Swedish certification body for
organic farming (KRAV, 2012) short time cultivars such as lettuce must have a
minimum pot size of 0.2 L, with a majority of nutrients coming from the growing
medium. This would mean that the organic nutrient solution is merely a comple-
mentary nutrient source. And although organic nutrient solution showed better
values than aquaculture water, they were not that far apart. Pantanella et al. (2012)
found that a balanced aquaponic system can accumulate minerals in amounts that
are on the same levels as those in conventional hydroponic nutrient solution, and
produce the same yields and quality of lettuce as conventional hydroponic cul-
tures. This means an aquaculture balanced to provide plant nutrients should be
more than adequate as a complementary nutrient source for organic hydroponic.
Of course the use of aquaculture effluents must also be accepted by organic stand-
ards for this resource to be utilized in certified organic cultures. KRAV (2012),
representing the Swedish certification body for organic farming, does not allow
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15
any feces or urine as fertilizer. This might rule out aquaculture effluents. The larg-
er volume of growing medium per pot in KRAVcertified greenhouse production
(KRAV, 2012) can also be an obstacle for adapting aquaponic cultures to this
standard. Optimizing the irrigation frequency can compensate for deficiencies in
the nutrient solution. The use of this tool can be restricted if container size and
growing medium do not allow good drainage and oxygenation. The important task
of ammonia assimilation and nitrification in the root environment will be de-
pressed by oxygen depletion. (Silber & Bar-Tal, 2008) Organic aquaponic cultiva-
tion is therefore dependent on a growing medium that fulfills the organic stand-
ards, supply adequate nutrients and allows for excellent drainage and aeration to
optimize nitrification and assimilation of nitrogenous waste and essential elements
by plants.
The low nutrient levels in the sampled aquaculture water could be explained by
high water exchange rate in combination with fish feed low on plant nutrients.
Levels of ammonia seemed to be very low, but still there were no indication of
nitrification process in the biofilter. But if nutrients were added as fish feed in the
main pools, and water removed during filtration process, chemical analysis should
have revealed significantly lower levels of essential elements after filtration. This
was not the case for any of the analyzed essential elements. One explanation could
be that the aquaculture facility was not recirculating water at all, or exchanging it
at high rates. In that case the sampling point that should have been after biofilter is
instead straight from the water source. This could explain why levels of fluores-
cent pseudomonades are higher in the rearing tank than in the inflowing water.
They grow faster in the rearing tank than the other analyzed microbial groups, in
contrast to being selectively removed by filtration. Sampling of the aquaculture
water source would have helped to reveal the actual circumstances.
5.2 Microbial densities
Because aquaculture water is polluted by fish waste, cfu was suspected to be high-
er than in the organic hydroponic. This proved to be false. The organic hydroponic
had higher density of aerobic bacteria and fluorescent pseudomonades, but similar
levels of fungi compared to aquaculture water. Density of fluorescent pseudomo-
nades varies between sample sites, being much lower at the biofilter outflow. This
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16
is interesting considering the importance of fluorescent pseudomonades in sup-
pressing plant pathogens (Haas & Dfago, 2005). Only fluorescent pseudomo-
nades were significantly lower, no changes in general bacteria or fungal cfu could
be found. One explanation for the reduced levels of pseudomonades could be if
this bacterial group was more abundant, compared to general bacteria and fungi,
on suspended solids than in free water. The significantly lower levels of organic
carbon support the idea that suspended solids were removed by mechanical filtra-
tion and sedimentation during the filtering process. But, as discussed above, the
overall impression from chemical analysis is that the sampled aquaculture facility
does not show the properties one could expect from a recirculating aquaculture
system. In that case total organic carbon is not removed by filtration; it was just
added by fish and feed in the rearing tank.
Qualitative analysis of microorganisms in an actual aquaponic farm would help
to better understand the composition of the micro flora in this unique environment
and its implications for nutrient cycling as well as plant health.
.
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17
6 Conclusion
1. Occurrence of aerobic bacteria was significantly higher in biosolid based nutri-
ent solution than in aquaculture water. Levels of fluorescent pseudomonades
were significantly different between all samples. Highest numbers were found
in the lettuce fertigator and least in biofilter effluents. No significant differ-
ences in regard to fungal cfu where found between any of the sampling sites.
2. The biosolid based nutrient solution was more nutritionally optimized than aq-
uaculture water. Aquaculture water from the sampling site was far from optimal
as nutrient source for lettuce cultivation, but so was the biosolid based nutrient
solution. Recirculated aquaculture water should be more than adequate, com-
pared to sampled organic nutrient solution, as a complementary nutrient source
in organic hydroponic.
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18
7 References
7.1 Literature
Atkin K, Nichols MA. (2004). Organic Hydroponics. Acta Hort 648:121-127.
Carruthers S. (2007). Challenges faced by the hydroponics industry worldwide. Acta Horticulturae:
742 :23-27.
FAO. (2006a). State of world aquaculture 2006. FAO Fisheries Technical Paper No. 500. Rome. 134
p.
FAO. (2011). World Aquaculture 2010. FAO Fisheries and Aquaculture Department. Technical Pa-
per No. 500/1. Rome, FAO. 118 p.
Hagopian DS, Riley RG. (1998). A closer look at the bacteriology of nitrification. Aquacultural En-
gineering 18: 223-244.
Haas D, Defago G (2005) Biological control of soil-borne pathogens by fluorescent pseudomonads.
Nat Rev Microbiology 3:307319
Koohakan P, Ikeda H, Jeanaksorn T, Tojo M, Kusukari S I, Okada K, Sato S. (2004). Evaluation of
the indigenous microorganisms in soilless culture: occurrence and quantitative characteristics in
the different growing systems. Scienta Hort. 101, 179-188.
KRAV. (2012). Vxtodling. In Regler fr KRAV certifierad produktion. 175 p.
Marschner H.(1995). Mineral Nutrition of higher plants. Academic Press Limited, London.
Pantanella E, Cardarelli M, Colla G, Rea E, Marcucci A.(2012). Aquaponic vs. hydroponics: produc-
tion and quality of lettuce crop. Acta horticulturae, 927:887-893.
Postma J. (2004). Suppressiveness of Root Pathogen in Closed Cultivation Systems. Acta Hort
644:503-510.
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Postma J, van Os E, Bonants P JM. (2008) Pathogen Detection and Managment Strategies in Soilless
Plant Growing Systems. In Soilles Culture: Theory and Practice (Raviv M, Heinrich Lieth J. ed.)
London, UK: Elsevier. pp.425-458
Rakocy JE, Shultz RC, Bailey DS, Thoman ES. (2004). Aquaponic Production of Tilapia and Basil:
Comparing a Batch and Staggered Cropping System. Acta Hort 648: 63-69
Rakocy JE, Masser M, Losordo TM (2006). Recirculating Aquaculture Tank Production Systems:
AquaponicsIntegrating Fish and Plant Culture. SRAC Publication 454:1-16.
Savidov N. (2004). Evaluation and Development of Aquaponics Production and Product Market
Capabilities in Alberta. Ids Initiatives fund Final Report. Project #679056201. August 17, 2004.
Savvas D. (2002) Hydroponic Production of Vegetables and Ornamentals (Savvas D. and Passam
H. ed.) Athens, Greece: Embryo Publications. ( pp. 15 -24).
Silber A, Bar-Tal A. (2008).Nutrition of Substrate-Grown Plants. Soilles Culture: Theory and Prac-
tice (Raviv M, Lieth J. ed.) London, UK: Elsevier. ( pp.291-339)
Sonnevald C, Straver N (1994). Nutrient solutions for vegetables and flowers grown in water or
substrates. Voedingsoplossingen glastuinbouw No. 8
Tyson RV, Treadwell DD, Simonne EH (2011). Opportunities and Challenges to Sustainability in
Aquaponic Systems. HortTechnology 21(1): 6-13.
Vallace J, Dniel F, Le Floch G, Gurin-Dubrana L, Blancard D, Rey P. (2010). Pathogenic and
benificial microorganisms in soilless culture. Agronomy for sutsainable development, INRA EDP
Sciences.
7.2 Manuals
HACH LANGE. Product information: Laboratory analysis and cuvette test. [Online.](2012-05-28).
Available at:
http://www.hach-
lange.co.uk/shop/action_q/download%3Bdocument/DOK_ID/14781331/type/pdf/lkz/GB/spkz/en
/TOKEN/UlbY1XH1gWo7pPh-beWgIrqhMic/M/8FiE9w